Method of making electrical circuit



Oct. 23, 1962 w. A. SEABURY m, ETAL 3,059,320

METHOD OF MAKING ELECTRICAL CIRCUIT Filed June 23, 1958 FIG. 1.

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FIG. 5.

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United States Patent METHOD OF MAKING ELECTRICAL CIRCUIT William A. Seabury IH, Ulster Park, and Robert D. Me-

Nutt, Kingston, N.Y., assignors to International BUSI- ness Machines Corporation, New York, N.Y., a corporation of New York Filed June 23, 1958, Ser. No. 743,682 11 Claims. (Cl. 29-155.5)

This invention relates to the manufacture of an insulating panel carrying an electrically conductive circuit, and pertains more specifically to a wholly mechanical method of manufacture for such panels which is readily adapted to automatic control.

Although it has hitherto been proposed to manufacture insulating panels carrying electrically conductive circuits, none of the methods previously known is readily subjected to automatic control directly from raw data which is supplied, for example, in the form of punched cards, or in any other conventional manner. Furthermore, many prior art processes have involved photography and/or electroplating steps which require expensive art Work and are difiicult to carry out so as to obtain the necessary uniformity of quality of product. Further, many of the prior processes have involved subjecting the entire face of the insulating panel to the action of an electrolytic solution or have involved coating the entire face of the insulating panel with an adhesive composition in order to secure the conductive circuit to it. These requirements have made it difiicult to maintain the desired insulating properties on the face of the panel which has been thus treated.

One object of the present invention is to provide a method of manufacturing insulating panels carrying electrically conductive circuits, which is readily subjected to automatic control directly from the raw data and which is free from electroplating and photographic steps.

Another object is to provide a method of manufacturing panels of the type described in which the adhesive composition employed to bond the circuit to the face of the panel is confined to that area of the panel which immediately underlies the circuit itself, thus making it unnecessary to control the electrical properties of the adhesive in order to maintain the desired insulating properties across the face of the panel.

Still another object is to provide a method of manufacturing panels of the type described in which automatic testing of the circuit may be carried out prior to bonding of the circuit to the insulating panel.

Other and further objects will be apparent from the drawing and the description which follows.

In the drawing:

FIG. 1 is a plan view showing a sheet of metal foil which has been punched to form a grid or reticulate sheet;

FIG. 2 is a view corresponding to FIG. 1, on an enlarged scale, showing the next step in the process in which residual webs, left during the first punching operation, are trimmed to form the desired lands;

FIG. 3 shows the step of applying to the grid of FIG. 2 a temporary support;

FIG. 4 shows the assembly after the next punching step which seve'rs the desired portions of the circuit from the undesired portions;

FIG. 5 shows the bottom plan view of the assembly of FIG. 4 after removal of the undesired portions of the circuit;

FlEG. 6 is a view in cross-section showing the step of bonding the circuit to the insulating panel;

FIG. 7 shows the step of removing the temporary support; and

P16. 8 is a plan view on an enlarged scale showing 3,059,320 Patented Oct. 23, 1962 the finished product with holes punched in the lands and insulating plate for mounting electrical components thereon.

In carrying out the process of the present invention, the first step is to design a wiring arrangement for the desired circuit so that the wiring connections all lie. on straight lines, which are either parallel or perpendicular to each other, forming a grid pattern. The termination points for the wiring paths, hereinafter referred to as lands, are the points at which the various electrical components are to be connected to the circuit, and these also must be arranged so as to lie along straight lines which are either parallel or perpendicular to each other and are intercalated in and connected to the first grid pattern defining the wiring connections.

The wiring pattern having been thus determined, it may be transferred to a sheet of conductive metal foil such as copper foil Iby punches, the operation of which is controlled by means of punched cards to provide the desired pattern.

The copper or other conductive metal foil employed to form the conductive circuit may be first coated, preferably on its rough or matte surface, with a thermosetting adhesive composition of conventional composition such as a phenol-aldehyde, urea-aldehyde, or melamine-aldehyde adhesive. The adhesive-coated foil is then subjected to a first punching operation, these punches being actuated to remove aligned rectangular areas from the foil and leave a grid pattern or reticulated sheet 10 of interconnected narrow bands of foil 14 as shown in FIG. 1. Certain of the rectangular areas, as determined by the automatic control are left unpunched to provide residual webs of foil 12 from which the desired lands or circuit terminal points may subsequently be formed. The grid of metal foil thus formed contains both the desired circuit and in addition a number of temporary bridges consisting of narrow bands of foil which serve to hold the grid together and locate its parts during this and certain subsequent steps of its manufacture.

The grid containing residual webs 12 is then subjected to a second punching operation to remove portions of the residual webs and leave the desired lands 15 in certain selected openings of the first grid pattern, which lands are connected to each other and to the first grid pattern by a second grid pattern consisting of narrow bands of foil 16, 18 intermediate between those formed during the first operation and parallel thereto. Consequently each of the lands is connected to the midpoint of each side of its respective opening by a narrow band 16, 18 of foil; The punches employed during this step need not be controlled by punch cards or the like, since they will have no effect on those areas which have been removed during the first punching operation. 7

There is then applied to the uncoated face of the grid shown in FIG. 2 an adhesive composition which is thermoreleasing, that is, which loses its' bonding strength when subjected to elevated temperatures sufficiently high to cure the thermosetting adhesive previously applied to the opposite face of the grid. The thermoreleasing adhee sive is selectively applied to the remaining lands by means of a die similar in construction to a rubber stamp having a protuberance at each possible land location, so that the remainder of the uncoated face of the grid remains free from any adhesive. Among suitable thermoreleasing adhesive compositions are gum arabic, polyvinyl alcohol, and gelatin, all of which may be applied to the lands in the form of an aqueous solution or dis-' persion.

A temporary supporting member 19 is then bonded to the raised portions of the lands by means of the thermo-' releasing cement, as shown in FIG. 3 of the drawing. The temporary supporting member maybe either electro conductive or electrically insulating and is preferably flexible. For example, aluminum foil, copper foil, or other metal foil may be used, or if desired, paper or other fibrous sheet material may be used impregnated with reinforcing resins if desired. In one embodiment of the present invention, electrically insulating temporary supporting sheet members such as paper sheets are preferred so that the continuity of the desired electrical circuit may be tested prior to its bonding to the insulating panel.

The grid, having been bonded to a temporary supporting member, is then subjected to another punching operation which is automatically controlled as by punched cards or the like. This punching operation, in which the punches penetrate both the electrically conductive sheet and the temporary supporting member, serves to sever the desired circuit or circuits from the undesired portion of the grid which has, as pointed out above, served to provide temporary bridges or temporary supports to locate all of the elements of the desired circuit in the proper positions with respect to each other.

The undesired or temporary bridge portions 20, 20 of the grid are now readily removed from the face of the temporary support 19 since they are not bonded to the support and are now free from connection with the lands 15 which are bonded to the support. This operation may be carried out manually or automatically, and in some cases suction devices may be found helpful in removing the unwanted portions of the grid. The resulting structure, as shown in FIG. 5, contains the desired lines and terminal points connected in the desired manner by narrow bands of foil, which represent the residue of the grids formed in the several punching steps. Inasmuch as each of the lands is bonded to the temporary support, the connecting lines or circuits are held in place solely by their connection to the lands. In the case where the temporary supporting member 19, or at least the face thereof in contact with the grid, is electrically insulating, the circuit may now be tested by an electroconductivity test through appropriately located electrodes. While the test may be carried out manually, it will be appreciated that it lends itself to automatic control from punched cards or the like.

The temporary support bearing the desire-d circuit on its face is then placed in contact with the desired insulating panel 22 as shown in FIG. 6, with the thermosettingadhesive-coated face of the circuit itself in direct contact with the panel, and with the temporary support continuing to maintain the desired circuits in their proper relationship with respect to each other. This assembly is then placed between the heated platens 24, 24 of a conventional hydraulic press and subjected to the heat and pressure required to cure the insulating panel and bond the circuit firmly to it by means of the thermosetting adhesive coating on the face of the circuit. Temperatures of the order of 310340 F. for 15 to 25 minutes at a pressure of the order of 900 to 1100 lb./ sq. in. are satisfactory for most conventional thermosetting adhesive compositions. During this step the circuit is embedded in the face of the insulating panel. Any of the conventional materials may be employed for the insulating panel itself, among the more common of which are paper or other fibrous sheet material impregnated with a thermosetting resinous composition such as phenolaldehyde, urea-aldehyde, melamine-aldehyde, or'other thermosetting resinous composition. The resinous composition may be previously cured, although it is preferably either uncured or only partially cured, as is the resin of the thermosetting adhesive composition, in order to provide a strong permanent bond between thev circuit and the panel, and to permit embedding of the circuit into the face of the panel. The same heating operation which serves to cure the thermosetting adhesive on the insulating panel serves to degrade the thermo-releasing adhesive which has securedthe temporary supporting member to the opposite face of the circuit. Consequently the temporary supporting member may now readily be stripped off from the face of the panel and circuit as shown in FIG. 7.

Any residual thermo-releasing adhesive which maybe present on the exposed face of the circuit may then be removed, as by brushing, burnishing or the like, and the holes 26 in the lands required for mounting the components of the circuit are punched through both the lands and the insulating panel in another automatically controlled punching operation to produce the product shown in FIG. 8.

It will be understood that the mounting of the components on the circuit and the soldering of these components may be carried out in any conventional manner, the soldering preferably being a single dip soldering step.

It will be appreciated that the coating of the grid or foil with thermosetting adhesive may take place at any time prior to bonding the grid to the insulating panel, either before or after any of the several punching operations and before or after bonding of the grid to the temporary supporting member. It is usually most convenient, however, to apply the thermosetting adhesive tothe foil prior to the first punching operation.

It will also be appreciated that the sequence of the first two punching operations may be reversed, with the step of delineating the lands 15 being carried out first. In this case this punching operation may be automatically controlled to delineate lands only in the desired locations, leaving the remainder of the sheet unpunched, so that it may be subjected to a second automatically controlled punching operation to form a second grid pattern, the resulting structure being identical with that shown in FIG. 2 of the drawing. It is also possible in this case to delineate lands throughout the full extent of the foil during the first punching operation, then remove only the undesired lands by the second, automatically controlled punching step; when this procedure is followed, the lands and both grid patterns are formed simultaneously in the first punching operation.

The automatically controlled punching operation or operations may be carried out by a single roving punch directed to specific locations and actuated by the data on punched cards. For most large-scale production operations, however, an array of punches is preferred, consisting either of a small number of rows (even a single row) of punches which are moved as a unit with respect to the foil to successive locations which are automatically controlled, or a complete array coextensive in area with the desired circuit, selected punches of the array being actuated by punched card control.

Although specific embodiments of the invention have been described herein, it is not intended to limit the invention solely thereto, but to include all of the obvious variations and modifications within the spirit and scope of the appended claims.

What is claimed is:

1. The method of making an insulating panel carrying an electrically conductive circuit which comprises providing a sheet of metal foil having one face coated with thermosetting adhesive, providing an array of punches adapted to punch a grid pattern from said sheet of metal foil, actuating selected punches of said array to form a metal foil grid having residual lands in a desired pattern and including both the desired circuit and temporary connecting bridges in said grid pattern, temporarily adhering the uncoated face of said residual lands to a temporary supporting member while leaving the remainder of said grid free from adhesion thereto, separating from the desired circuit and residual lands the undesired portion of said grid, bonding the coated face of said desired circuit and residual lands to an insulating panel, and releasing the temporary supporting member from said residual lands.

2. The method of making an insulating panel carrying an electrically conductive circuit which comprises providing a sheet of metal foil having one face coated with thermosetting adhesive, punching from said sheet a grid pattern having residual lands in a desired array and including both the desired circuit and temporary connecting bridges in said grid pattern, applying to the residual land portions only of the uncoated face of said grid pattern an adhesive which is releasable upon heating, and bonding to said residual land portions with said adhesive a temporary supporting member, punching said grid pattern on said supporting member to separate the undesired portion of the grid pattern from the desired circuit and from the residual lands, heating and pressing the desired circuit and residual lands against an insulating panel while said circuit and lands are still adhered to said temporary supporting member, said heat and pressure serving to bond said circuit and lands to said insulating panel and to release the lands from said temporary supporting member, and removing said temporary supporting member from said lands.

3. The method as defined in claim 2 including in addition the step of cleaning the exposed face of said lands and circuit after removal of said temporary support to remove any residual adhesive.

4. The method as defined in claim 2 in which said insulating panel comprises a thermosetting resin.

5. The method as defined in claim 4 in which said resin is thermoset at least in part during the step of bonding the circuit and lands to said insulating panel.

6. The method of making an insulating panel carrying an electrically conductive circuit which comprises punching a sheet of electrically conducting material in a predetermined pattern to form lands and relatively narrow strips of said material connecting said lands to the margins of said sheet, said lands and said strips comprising the conductive elements of said circuit and additional temporary connecting bridges, temporarily securing a supporting member to one face of said punched sheet only in portions which are comprised in the conductive elements of said circuit, punching said assembly to sever said elements from the remainder of said strips so that said remainder is freely removable from said support while said elements remain adhered thereto, securing the opposite face of said portions to a face of said insulating panel and removing said temporary support from said portions,

7. The method according to claim 6 in which said first punching is performed by mechanism adapted to punch said sheet in uniformly spaced and sized areas to remove said areas leaving intervening portions of said sheet as portions of certain of said strips, said machine being controllable to omit said punches in those said areas forming lands in the electrically conductive circuit.

8. The method according to claim 7 wherein adhesive is applied to said punched sheet for temporarily securing the sheet to said support member by an applicator adapted to apply said adhesive only in said areas so that said adhesive is applied only to said areas forming lands.

9. The method according to claim 7 wherein said sheet, after said first punching, is subjected to the action of punches acting only in said areas and effective to form said previously unpunched areas into reduced lands and strips connecting said lands to contiguous strips.

10. The method according to claim 6 wherein said punching of said assembly of said sheet and said temporary base is performed by mechanism controllable to punch said assembly to sever only certain of said strips at their juncture with said portions forming the conductive elements of said circuit.

11. The method according to claim 6 which includes the step of applying to one face of said sheet preliminary to punching a thermo-setting adhesive which is utilized to secure to said panel said face of the portions thereof forming the conductive elements of said circuit, and wherein the opposite face of some of said portions is adhesively united to said temporary supporting member by an adhesive which is thermo-releasing at a temperature at which said first adhesive is thermo-setting.

References Cited in the file of this patent UNITED STATES PATENTS 

